Keys, SumIndexFields, and TableRelations in our examples

So far, we have created basic table definitions and associated pages for the WDTU project. The next step is to flesh out those definitions with additional keys, SIFT field definitions, table relations, and so on. The purpose of these are to make our data easier and faster to access, to take advantage of the special features of NAV to create data totals, and to facilitate relationships between various data elements.